The present invention relates to barcode reading techniques, and more particularly, to a method and system for sensing a barcode, especially when the resolution of the signal is low and/or the noise is large.
During a process for sensing a barcode 10 (FIG. 1a), an analog optical signal obtained by a barcode reader or scanner is usually digitized by a digitizer into a digital signal, e.g., into a square wave form. A proper threshold (gate level) of the digitizer is adopted so as to effectively separate the signal from the noise, as shown in FIGS. 1b-1f in which various scenarios are schematically illustrated. In FIGS. 1b-1f, the digitized results 3 and 4 correspond to the higher and lower thresholds 2 and 1 respectively. When the resolution of the signal 20 is high and there is no noise, both higher and lower thresholds 2 and 1 can generate correct result 3, 4 (see FIG. 1b). When the resolution of the signal 20 is low and the noise 30 is small, a lower threshold 1 shall be used so as not to miss some of the signal elements, e.g., 20a and 20b (see FIG. 1c). When the resolution of the signal 20 is high but the noise 30 is also large, a higher threshold 2 shall be used so as not to generate false results from the noise (see FIG. 1d). In any of the above circumstances, the signal can be effectively separated from the noise by selecting a proper threshold.
However, when the resolution 20 is low but the noise 30 is large, the amplitudes of some signal elements 20a, 20b may be close to that of the noise 30, as illustrated in FIG. 1f, thus the signal 20 cannot be effectively separated from the noise by either a higher or a lower threshold 2 or 1. This may happen in the circumstances where the barcode 10 is in a defocus area of the light beam or in a long distance area from the reader, or the barcode is printed with a high density of elements (i.e., bars 11 and spaces 12).
Therefore, there exists a need for a solution that can effectively eliminate the noise from the signal during the digitization process so as to generate a correct digitized output, especially when the noise is of a similar level to the signal of low resolution.